1. Field of the Invention
The present invention relates to a laser device and an optical amplifier. Particularly, the present relates to a laser device and an optical amplifier equipped with a plurality of solid gain media.
2. Description of the Related Art
Laser media having wide emission wavelength bands are favorably used in short pulse lasers (mode locked lasers). Materials to which Yb (ytterbium) ions, which are rare earth ions, are added (as disclosed in “Femtosecond Yb:YAG laser using semiconductor saturable absorbers”, C. Honninger et al., Optics Letters, Vol. 20, No. 23, pp. 2402-2404, 1995), glass to which Nd (neodymium) ions are added (as disclosed in Japanese Unexamined Patent Publication No. 6 (1994)-244486), and materials to which Ti (titanium) ions, which are transition metal ions, are added (as disclosed in U.S. Pat. No. 6,618,423) are known laser media having wide emission wavelength bands, particularly as solid laser media (solid gain media). Fibers to which Er (erbium) is added (as disclosed in U.S. Pat. No. 5,689,519) and the like are known as laser media having wide emission wavelength bands, as fiber lasers. Short pulse lasers of the p (pico) second and f (femto) second class require laser media having extremely wide emission wavelength bands. Therefore, conventional short pulse lasers of these classes were limited to employing laser media such as those described above, that is, the wavelengths of the lasers were limited to the infrared range. In addition, four level system Nd ions, which are advantageous in laser emission within the 1 μm band, have narrow emission widths if used with YAG (Y3Al5O12) as the base material, and cannot be utilized for short pulse lasers. Accordingly, glass base materials are used with these ions, in order to widen the emission width. However, glass has a low coefficient of thermal conduction, and therefore there is a problem that Nd ion added glass solid lasers are not suited for high output laser emission.
Various methods, such as those employing semiconductor lasers, pigment lasers, Ti:Sapphire lasers, and OPO (Optical Parametric Oscillators) have been proposed to realize wavelength variable lasers. Particularly, many wavelength variable lasers employing semiconductor lasers are currently being developed. However, the emission ranges of these lasers are mostly within the infrared-near infrared range, and emission in only blue and violet color ranges have been realized within the visible light spectrum. Ti:Sapphire lasers are commonly employed as wavelength variable lasers, but the emission wavelengths thereof are limited to the near infrared range. These infrared-near infrared range emitting lasers are able to emit light within the visible light spectrum by utilizing SHG (Second Harmonic Generation). However, laser emission within the visible light spectrum utilizing SHG cannot realize high efficiency nor stable operation. In contrast, pigment lasers have a mean variable wavelength range of approximately 50 nm in the case that a single pigment is employed, but it is possible to emit laser light within the ultraviolet-infrared wavelength range by utilizing a plurality of types of pigment. However, pigments have the problem that they deteriorate, and a drawback that pump light sources are expensive for shorter wavelengths. Meanwhile, OPO's are capable of covering a comparatively wide variable wavelength range, but there are problems, such as beam quality. Accordingly, there are advantages and drawbacks to currently available variable wavelength lasers, and industrial application thereof is difficult.
As described above, there is demand for a device which is capable of stably emitting laser light across a wide spectral band ranging from infrared through the visible light spectrum as either a short pulse laser or as a variable wavelength laser. In addition, there is similar demand for an optical amplifier for amplifying laser beams.